Would love to get down to South America one year and climb a big mountain down that way. Aconcagua has occupied some of my thoughts but Cotopaxi had to be awesome. Have always heard great things about it.
Katahdin is a cool mountain as well. I got my start as a Northeast hiker 20-something years ago and have had several trips to Baxter Stae Park. Did Katahdin via the Abol Slide route back in '96 or so.
And yeah, I get the routes versus mountains thing. But really I was just trying to differentiate in my OP between day-hiking your local hill and big mountains. I know Rainier isn't the world's most technically difficult mountain, but by any route it is a multi-day venture that requires roped glacier travel and 9K or so feet of vertical ascent. Personally, I get most excited in the Class 3 or 4 category. Of the mountains I listed in my OP, Rainier has the softest max angle at 35 degrees or so via its easier routes. The others I mentioned get to 55 degrees or so via the routes I took except for Granite, which had low Class 5.
Anyway, cool to see other climbers on here.